Polymer compositions and absorbent fibers produced therefrom

ABSTRACT

Aqueous, uncured but curable, polymer compositions which are stable at room temperature and possess excellent shelf life in uncured form are disclosed. The uncured polymer compositions can be made into fibers using conventional fiber forming processes and cured to produce absorbent fibers capable of absorbing at least 60 times their weight of brine.

This is a division of application Ser. No. 07/460,681, filed Jan. 4,1990, now U.S. Pat. No. 5,026,784.

This invention relates to curable polymer compositions which, whencured, become highly water absorbent.

More specifically, this invention relates to aqueous uncured linearpolymer compositions which are stable at room temperature and possessexcellent shelf life in uncured form. Because of their excellent shelflife, the compositions can be made into fibers which become highly waterabsorbent when cured.

In one of its more specific aspects, this invention relates to highlyabsorbent fibers and fiber products suitable for use in the manufactureof conventional hygienic and household absorbent products. The fibers ofthis invention achieve uniformly consistent, highly absorbent propertiesusing small amounts of a reactive cross-linking compound and requireshort cure times.

The terms "absorbent," "water-absorbing," and "water-absorbent" whenused herein to modify the polymer compositions, fibers, or fiberproducts of this invention are meant to include water, brine, andelectrolyte solutions such as body fluids.

Absorbent polymers in powder form are widely used in hygienic andhousehold products. Examples of such products include surgical anddental sponges, tampons, sanitary napkins and pads, bandages, disposablediapers, disposable towels, incontinence products, meat tray pads,household pet litter, and the like. Absorbent polymers are also used assoil conditioners to improve water retention and increase air capacityand as water stopping agents for cables and the like.

Although many of the commercial absorbent powders exhibit goodwater-absorbing capacity, they are hard to incorporate into absorbentproducts (e.g., disposable diapers) because of powder dusting problemsand their tendency to move from where are placed. Special powderhandling equipment is generally required, and the powder must be glued,fused, or laminated to a support structure to keep the powder in place.These additional handling and manufacturing steps are time-consuming andincrease manufacturing and product costs. In addition, powders form gelsthat have little integrity or gel strength, and because of this, theyare difficult to contain within a support structure. The containment ofan absorbent material and the gel it forms upon absorbent usage is acritical property of disposable products.

The above deficiencies in absorbent powders have led the absorbentproduct industry to seek non-powder forms of absorbent resins,specifically fibers. There remains a need in the absorbent productindustry for an absorbent fiber which possesses uniformly consistentabsorbent properties and can be made reliably at high speed and in largevolume, using, to the extent possible, conventional spinning technology.It is obvious that the industry also desires higher absorbing fibers.

One recent approach suitable for producing absorbent powders but notfibers is found in U.S. Pat. No. 4,418,163. This patent teaches a highlyabsorbent resin obtained by adding a polyamine to the reaction productof an isobutylene-maleic anhydride copolymer with an alkali metalhydroxide. Cross-linking is achieved by ionic bonds between the carboxylgroups and the polyamine which bonds form immediately and at roomtemperature. The ionic bonds are converted to amide linkage bydehydration, resulting in an absorbent resin. Due to the immediate ionicbond-forming reaction which serves to insolubilize the polymer, furtherprocessing of the resin into fibers is not feasible. Cross-linkingagents other than polyamines are disclosed, including polyhydricalcohols and amino-alcohols, but the patent further teaches that if across-linking agent other than a polyamine is used, cross-linking isthen effected by linkages which are liable to hydrolysis, resulting invery poor water-absorbing composites. U.S. Pat. No. 4,418,163, is notseeking to produce fibers and fails to recognize that the key toproducing absorbent fibers lies in the use of different cross-linkingchemistry. Moreover, the very benefit sought and achieved by using apolyamine in the patent leads away from fiber manufacture.

U.S. Pat. Nos. 4,731,067 and 4,880,868 to Bi Le-Khac teach that blendsof partially neutralized isobutylene-maleic anhydride copolymers andnon-reactive compounds can be made into absorbent fibers. Morespecifically, Le-Khac discovered that blends of a diol or glycol with apartially neutralized isobutylene-maleic anhydride copolymer are stableat room temperature, can be stored for long periods of time, andfacilitate fiber spinning on conventional spinning equipment. Fiberspinning of Le-Khac's blends is possible because cross-linking iseffected only through ester linkages which do not form at roomtemperature, giving the blends excellent stability and shelf life.

Notwithstanding the significance of Le-Khac's discovery thatcross-linking through ester linkages results in a stable, uncured butheat curable syrup which can be spun into fibers using conventional dryspinning techniques, the resulting fibers have met with limitedcommercial success. The limited commercial success is due to the factthat the absorbent properties of the fibers are extremely difficult tocontrol; there is considerable absorbency variation between fibers andamong fiber runs. This difficulty in controlling the absorbentproperties of the fibers is due in large part to the fact that in orderto achieve cross-linking cure times of about thirty minutes and obtain afiber that absorbs 40-50 times its weight of brine, it is necessary toadd considerably more diol or glycol than is theoretically needed toachieve cross-linking. The addition of excess amounts of diol or glycolare necessary because during processing, i.e., spinning of the blend,large amounts of the non-reactive diol or glycol are washed out of theblend or tend to migrate to the fiber surface and do not effectcross-linking. In other words, extra diol or glycol must be added toensure that sufficient amounts are present to achieve cross-linking ofthe resultant fibers. Because of the excess amount and uncertainlocation of non-reactive compound in the fiber and on the fiber surface,absorbency properties of the fibers are difficult to control and tend tovary considerably. Obtaining optimal curing and consistent absorbency ispretty much by trial and error.

A substantial amount of additional effort has gone into understandingthe cross-linking problems exhibited by the fibers of theabove-mentioned patents and has led to the discovery of not only thereasons for the problems but also to the present invention, whichprovides a solution to those problems. The present invention facilitatesthe production of absorbent fibers using conventional spinningequipment, requires considerably less cross-linking agent, shorter curetimes, and yields absorbent fibers having uniformly consistentabsorbency properties. Quite surprisingly, the absorbent fibers of thisinvention possess much better absorbent properties as compared to theprior art fibers.

According to this invention, there is provided a fiberizable, aqueous,uncured but curable, polymer composition comprising the reaction productof:

(a) a partially neutralized aqueous polymer composition prepared by thereaction of a strong base with a polymer containing at least 25 molepercent recurring units of an α, β-unsaturated monomer having in itsmolecule one or two carboxyl groups or one or two other groupsconvertible to carboxyl groups, the degree of neutralization of saidpartially neutralized polymer being within the range of from about 0.2to about 0.8 equivalent of total carboxyl groups or groups convertibleto carboxyl groups of the α,β-unsaturated monomer, with

(b) from about 0.1 to about 10 total parts by weight of at least onereactive compound per 100 parts by weight of the partially neutralizedaqueous polymer, the reactive compound being a water soluble compoundbearing one amine group and at least one hydroxyl group, wherein thereaction product is formed by substituted ammonium carboxylate ionicbonding between the unneutralized carboxyl groups on the polymer and theamine groups on the reactive compound.

Also according to this invention, there is provided a method for makingabsorbent fibers which comprises:

(a) attenuating a partially neutralized, aqueous, uncured polymercomposition prepared by reacting a strong base with a polymer containingat least 25 mole percent recurring units of an α,β-unsaturated monomerhaving in its molecule one or two carboxyl groups or one or two othergroups convertible to carboxyl groups, the degree of neutralization ofsaid partially neutralized polymer being within the range of from about0.2 to about 0.8 equivalent of total carboxyl groups or groupsconvertible to carboxyl groups of the α,β-unsaturated monomer, with fromabout 0.1 to about 10 total parts by weight of at least one reactivecompound per 100 parts by weight of the partially neutralized polymer,the reactive compound being a water soluble compound bearing one aminegroup and at least one hydroxyl group, and

(b) heating the fibers to cure and render them absorbent by removingwater and cross-linking through both ester and amide linkages.

According to this invention, there is also provided an absorbent fiberwhich is the cured attenuated reaction product of:

(a) a partially neutralized, aqueous, uncured polymer compositionprepared by reacting a strong base with a polymer containing at least 25mole percent recurring units of an α,β-unsaturated monomer having in itsmolecule one or two carboxyl groups or one of two other groupsconvertible to carboxyl groups, the degree of neutralization of saidpartially neutralized polymer being within the range of from about 0.2to about 0.8 equivalent of total carboxyl groups or groups convertibleto carboxyl groups of the α,β-unsaturated monomer, with

(b) from about 0.1 to about 10 total parts by weight of at least onereactive compound per 100 parts by weight of the partially neutralizedaqueous polymer, the reactive compound being a water soluble compoundbearing one amine group and at least one hydroxyl group.

In a preferred embodiment, cured fibers of this invention are capable ofabsorbing at least 60, preferably at least 70, and most preferably atleast 80, times their weight in brine (0.9 wt. % NaCl) and are producedusing from about 0.1 to about 10, preferably from about 0.5 to about 6,and most preferably from about 1 to about 5, parts by weight of reactivecompound and cure conditions within the following ranges: curetemperature, 140°-210° C.; cure time, less than about 15, preferablyless than about 12, minutes. The examples which follow below demonstrateseveral fibers which fall within the preferred embodiment.

The partially neutralized polymer employed in this invention is preparedusing a polymer containing at least 25 mole percent recurring units ofα,β-unsaturated monomer. The polymer may be a homopolymer or acopolymer, in which case it will contain in mole percent from about 25to about 75 mole percent of at least one α,β-unsaturated monomer andfrom about 75 to about 25 recurring units of at least onecopolymerizable monomer.

Any α,β-unsaturated monomer having in its molecule one or two carboxylgroups or one or two other groups which can be converted into carboxylgroups by hydrolysis or acidification is suitable for use.

Particularly suitable α,β-unsaturated monomers for use to producehomopolymers usable to produce the partially neutralized polymer includeacrylic acid and methacrylic acid.

Particularly suitable α,β-unsaturated monomers for use to producecopolymers usable in this invention include those which bear one or twocarboxyl groups or groups convertible to carboxyl groups, such ascarboxylic acid salt groups, carboxylic acid amide groups, carboxylicacid imide groups, carboxylic acid anhydride groups, and carboxylic acidester groups.

Examples of suitable α,β-unsaturated monomers are maleic acid, crotonicacid, fumaric acid, mesaconic acid, the sodium salt of maleic acid, thesodium salt of 2-methyl,2-butene dicarboxylic acid, the sodium salt ofitaconic acid, maleamic acid, maleamide, N-phenylmaleimide, maleimide,maleic anhydride, fumeric anhydride, itaconic anhydride, citraconicanhydride, mesaconic anhydride, methyl itaconic anhydride, ethyl maleicanhydride, diethylmaleate, methylmaleate, and the like, and theirmixtures.

Suitable copolymerizable monomers for use to produce partiallyneutralized copolymers used in this invention can be readily selected byone skilled in the art. Of course, a copolymerizable monomer which doesnot negatively affect the absorbent properties of the cured reactionproduct should be selected.

Suitable copolymerizable monomers include α-olefins, vinyl monomers, andvinylidene monomers. Examples of suitable monomers include: ethylene,propylene, isobutylene, 1-butylene, C₁ to C₄ alkyl methacrylates, vinylacetate, methyl vinyl ether, isobutyl vinyl ether, and styreniccompounds having the formula: ##STR1## wherein R represents hydrogen oran alkyl group having from 1 to 6 carbon atoms and wherein the benzenering may be substituted with low molecular weight alkyl or hydroxygroups.

Suitable C₁ to C₄ alkyl acrylates include methyl acrylate, ethylacrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, andthe like, and their mixtures.

Suitable C₁ to C₄ alkyl methacrylates include methylmethacrylate, ethylmethacrylate, isopropyl methacrylate, n-propylmethacrylate, n-butylmethacrylate, and the like, and their mixtures.

Suitable styrenic compounds include styrene, α-methylstyrene,p-methylstyrene, t-butyl styrene, and the like, and their mixtures.

If a copolymer (understood to include terpolymers, etc.) rather than ahomopolymer is employed in the practice of this invention, it willcontain in mole percent from about 25 to about 75 recurring units of atleast one α,β-unsaturated monomer and from about 75 to about 25recurring units of at least one copolymerizable monomer. Preferably, thecopolymer will contain from about 35 to about 65 mole percent recurringunits of at least one α,β-unsaturated monomer and from about 65 to about35 total mole percent of at least one copolymerizable monomer. Mostpreferably, the copolymer used in the invention will be an equimolarcopolymer. Copolymers are preferred in the practice of this invention.

Examples of polymers usable in the practice of this invention include:α-olefin/maleic anhydride copolymers, α-olefin/citraconic anhydridecopolymers, α-olefin/acrylic acid copolymers, α-olefin/methacrylic acidcopolymers, vinyl compound/maleic anhydride copolymers, vinylcompound/citraconic anhydride copolymers, vinyl compound/acrylic acidcopolymers, vinyl compound methacrylic acid copolymers, alkylacrylate/maleic anhydride copolymers, alkyl acrylate/citraconicanhydride copolymers, alkyl vinyl ether/maleic anhydride copolymers,alkyl vinyl ether/citraconic anhydride copolymers, vinyl acetate/maleicanhydride copolymers, α-olefin/maleic anhydride/α-olefin terpolymers,polyacrylic acid, polymethacrylic acid, and the like, and theirmixtures.

One polymer particularly suitable for use in this invention is acopolymer of isobutylene and maleic anhydride. Another is styrene andmaleic anhydride. Suitable polymers will have peak molecular weights offrom about 5,000 to about 500,000 or higher.

Copolymers of isobutylene and maleic anhydride can be prepared using anysuitable conventional method but are also commercially available fromKuraray Isoprene Chemical Company, Ltd., Tokyo, Japan, under thetrademark ISOBAM. ISOBAM copolymers are available in several gradeswhich are differentiated by viscosity molecular weight: ISOBAM-18,290,000 to 310,000; ISOBAM-10, 160,000 to 170,000; ISOBAM-06, 80,000 to90,000; ISOBAM-04, 55,000 to 65,000; and ISOBAM-600, 6,000 to 10,000.ISOBAM-18 and ISOBAM-10 are the preferred copolymers.

As discussed above, an α,β-unsaturated monomer which contains one or twogroups convertible to the required carboxyl groups may be used, butconversion typically involves an additional hydrolysis or acidificationstep.

For example, if the α,β-unsaturated monomer bears only carboxylic acidamide, carboxylic acid imide, carboxylic acid anhydride, carboxylic acidester groups, or mixtures thereof, it will be necessary to convert atleast a portion of such carboxylic acid derivative groups to carboxylicacid groups by, for example, a hydrolysis reaction. If anisobutylene/maleic anhydride copolymer is selected for use, upon theformation of an aqueous composition, a ring-opening hydrolysis reactionoccurs which provides a pendant carboxyl group.

The neutralization reaction to produce the partially neutralized polymerused in this invention is carried out using any suitable strong organicor inorganic base. Suitable bases include alkali metal hydroxides,ammonium hydroxides, and substituted ammonium hydroxides. Alkali metalhydroxides such as potassium hydroxide and sodium hydroxide arepreferred.

The neutralization reaction is carried out in water to obtain apartially neutralized polymer, the degree of neutralization of thepolymer being within the range of from about 0.2 to about 0.8,preferably 0.3 to 0.7, equivalent of total carboxyl groups of theα,β-unsaturated monomer.

In the practice of this invention, the partially neutralized polymer isthen reacted with from about 0.1 to about 10 or more, preferably fromabout 0.5 to about 6, and most preferably from about 1 to about 5, partsby weight of a reactive compound selected to have one amine group and atleast one, preferably two, hydroxyl groups per 100 parts by weight ofpartially neutralized polymer. Using more than 10 parts of reactivecompounds, although possible, provides no advantage in this invention.Moreover, it is desirable to use as little reactive compound as possiblesufficient to achieve cross-linking.

Suitable water-soluble reactive compounds include: ethanolamine,tris(hydroxymethyl)aminomethane, 3-amino-l-propanol,DL-1-amino-2-propanol, 2-amino-l-butanol, N,N-dimethylethanolamine,diisopropanolamine, methyldiethanolamine, triethanol amine,2-(methylamino)ethanol, and the like, and their mixtures.Tris(hydroxymethyl)aminomethane is preferred.

The water-soluble reactive compound bearing one amine and at least onehydroxyl group serves as a high temperature, slow-reacting, two-stepcross-linking agent for the partially neutralized polymer. The aminegroups react first to tie or graft the reactive compound onto thepartially neutralized polymer via fast-reacting ammonium salt formationsbetween the amine and the pendant carboxylic acid units on the polymer.At this point, the partially neutralized polymer reaction product isstill linear and possess excellent shelf life stability andprocessability. It is not cured, and hence, not absorbent, at this pointand can be fabricated into any desired form for absorbent usage, such asfibers. The resultant ionic bonds are sufficient to keep the reactivecompound from migrating to the fiber surface or washing out during fiberprocessing; thus, there is no need to employ the reactive compound inexcess. All of the reactive compound remains available for thecross-linking reaction.

The second stage reaction between the reactive compound and the polymeris the curing or cross-linking reaction. This cross-linking reactionwill not occur and the product will not become absorbent until thepartially neutralized polymer reaction product, bearing grafted reactivecompound, is heated to a temperature sufficient to (i) remove water andform ester linkages between the hydroxyl groups of the reactive compoundand the carboxy groups of the polymer and (ii) convert the substitutedammonium carboxylate ionic bonds to amide linkages.

The cure conditions required to achieve optimal cross-linking dependsupon several factors, including the particular polymer employed. Forexample, the cure temperature will depend on the polymer. If thecopolymer is a partially neutralized ethylene/ maleic anhydridecopolymer, a cure temperature of at least 140° C. will be required toachieve cross-linking. If the copolymer is a partially neutralizedstyrene/maleic anhydride copolymer, a temperature of at least about 150°C. is required to cross-link; and if a partially neutralizedisobutylene/maleic anhydride copolymer is employed, a temperature of atleast about 170° C. will be required to achieve cross-linking. Curetimes can vary depending, of course, on cure temperature and on theamount of reactive compound used. Cure times will typically be withinthe range of from about 0.5 to about 20 minutes, preferably 0.5 to 15minutes, and most preferably 0.5 to 12 minutes. To maximize absorbentproperties, optimal cure of the fibers (i.e., minimal amount ofcross-linking needed to form a cross-linked network) is required.Optimal cure is achieved by adjusting a number of variables within wideranges depending upon the specific syrup composition. As will be shownin the examples which follow, optimal cure conditions require, amongother things, a balance between cure time and cure temperature.

As is readily apparent from the high temperature required to achievecross-linking, the aqueous reaction product of the partially neutralizedpolymer and the reactive compound, i.e., the grafted polymer syrup, canbe stored for an unlimited time. This unlimited room temperaturestability facilitates further processing of the syrup into any number ofconventional forms, such as fibers and films using conventional methods.For example, the syrup can be further processed by casting, spraydrying, air-assisted spray drying, air attenuation, wet spinning, dryspinning, flash spinning, and the like. To facilitate the removal ofwater from the aqueous composition of this invention during the spinningprocess, minor amounts of other polar solvents such as alcohol can beadded to the aqueous syrups of the invention. The resultant fibers canbe further processed into milled fibers, chopped fibers, fluff or bulkfibers, strands, yarns, webs, composites, woven fabrics, non-woven mats,tapes, scrim, and the like, using a variety of methods includingtwisting, beaming, slashing, warping, quilling, severing, crimping,texturizing, weaving, knitting, braiding, etc., and the like.

All fiber samples produced in the examples which follow were tested todetermine their absorbent properties using conventional test proceduresto measure the unit of liquid (brine) absorbed per unit of fiber sample(Free Swell Index) and the unit of liquid (brine) retained per unit offiber sample after subjecting the swelled fiber sample to 0.5 psi. Inaddition, all fiber samples were felt after cure to determine whethereach sample was slippery to the touch (S) indicating undercure, dry tothe touch (D) indicating full cure, or very dry to the touch (VD)indicating overcure. The Free Swell Index test procedure used isdescribed in U.S. Pat. No. 4,454,055, the teachings of which areincorporated herein by reference. The test procedure and equipment usedherein were modified slightly as compared to the procedure and equipmentdescribed in U.S. Pat. No. 4,454,055.

To determine the Free Swell Index at atmospheric (room) pressure, about0.2 to 0.3 g of about 3/4 in. cured water-absorbing fibers to be testedis placed in an empty W-shaped tea bag. The tea bag containing thefibers is immersed in brine (0.9 wt. % NaCl) for 10 minutes, removed andallowed to sit on a paper towel for 30 seconds to remove surface brine.The Free Swell Index of the fiber, that is, the units of liquid absorbedper each unit of sample is calculated using the following formula:##EQU1##

To determine Free Swell Index under pressure (0.5 psi retention), thefollowing modified procedure was used.

After the tea bag containing the fiber sample is immersed in brine andsurface brine is removed, it is immediately placed in a 16 cm ID Buchnerfunnel fitted with a 2000 ml sidearm vacuum filter flask and connectedto a manometer. A piece of dental dam rubber sheeting is securely fixedover the mouth of the funnel such that the sheeting just rests on thetea bag. Next, a vacuum sufficient to create the desired pressure isdrawn on the flask for a period of 5 minutes, and the Free Swell Indexunder pressure is calculated using the above formula.

The following examples further demonstrate the invention.

EXAMPLE 1

This example demonstrates the preparation of an uncured syrupcomposition of this invention and further demonstrates the preparationof cured absorbent fibers from the syrup composition.

A syrup composition (Syrup A) was prepared by reacting about 2.96 grams(2 phr) of a water-soluble reactive compound,tris(hydroxymethyl)aminomethane, with about 400 grams of a partiallyneutralized isobutylene/maleic anhydride copolymer solution. Thepartially neutralized isobutylene/maleic anhydride copolymer solutionwas prepared as follows.

About 148.2 lbs. of demineralized water were added to a 50-gallon Rossmixer. Next, about 31 lbs. of sodium hydroxide pellets were added slowlyto the mixer with agitation. About 108.5 lbs of ISOBAM-10isobutylene/maleic anhydride (1:1) copolymer were charged into the mixerover a period of about one hour with agitation. ISOBAM-10 copolymer hasa viscosity molecular weight of about 170,000 and is commerciallyavailable from Kuraray Isoprene Chemical Company, Ltd. After theaddition of ISOBAM-10 copolymer, the mixer contents were heated to about100° C. and held with continuous agitation for about four hours tocomplete the neutralization reaction.

Syrup A was observed to be non-cross-linked and found to be stable atroom temperature. Syrup A was also found to contain 48% solids and havea pH of 6.8. The degree of neutralization was found to be about 0.55,meaning 55% of carboxyl groups had been neutralized, with 45% remainingunneutralized carboxylic acid units.

Fibers were spun from Syrup A using a dry spinning process. The fibersproduced had deniers of 2-3 and were non-cross-linked.

The fibers were divided into several portions and each portion wasseparately cured by heating at about 180° C. for different cure timeswithin the range of from about 10 to about 20 minutes. Each portion ofcured fibers was recovered as water-absorbing fibers of the inventionand tested for brine absorbency. The cure conditions and brineabsorbency test results are shown in Table I.

                  TABLE I                                                         ______________________________________                                        FIBER CURE CONDITIONS AND BRINE ABSORBENCY                                    PROPERTIES                                                                    Fibers of Syrup                                                                            A       A       A     A     A                                    ______________________________________                                        Cure Temperature                                                                           180     180     180   180   180                                  (°C.)                                                                  Cure Time (Minutes)                                                                        10      10      14    18    20                                   Absorbency Test:                                                              Swell Index                                                                   Atm. Pressure (g/g)                                                                        100.5   95.6    80.6  76.5  69.9                                 0.5 psi (g/g)                                                                              72.5    66.6    55.6  48.9  42.6                                 Cure State   D       D       D     D     D/VD                                 ______________________________________                                    

The above data show that using 2 phr of reactive compound and a curetemperature of 180° C. fully cured fibers having excellent absorbencyare produced. The data further show that absorbent properties decreaseas cure times are lengthened, indicating that cure times of about 10minutes or less at 180° C. and 2 phr cross-linking agent are optimal.

EXAMPLE 2

This example demonstrates the preparation of another uncured syrupcomposition of this invention (Syrup B) using substantially theprocedure of Example 1 but employing 5.92 grams (4 phr) oftris(hydroxymethyl)aminomethane reactive compound.

Syrup B was likewise observed to be non-cross-linked and found to bestable at room temperature.

Fibers of 2-3 denier were spun from Syrup B using a dry spinningprocess. The uncured fibers were divided into several portions forcuring, and each portion was cured and tested to determine its absorbentproperties. The cure conditions and brine absorbent properties are shownin following Table II.

                                      TABLE II                                    __________________________________________________________________________    FIBER CURE CONDITIONS AND BRINE ABSORBENT PROPERTIES                          Fibers of Syrup                                                                           B   B   B   B   B   B   B                                         __________________________________________________________________________    Cure Temperature (°C.)                                                             180 185 180 185 180 180 180                                       Cure Time (Minutes)                                                                       5   5   7.5 7.5 8.7 10  15                                        Absorbency Test:                                                              Swell Index                                                                   Atm. Pressure (g/g)                                                                       85.7                                                                              67.3                                                                              79.7                                                                              51.7                                                                              69.9                                                                              63.8                                                                              57.5                                      0.5 psi (g/g)                                                                             49.6                                                                              45.9                                                                              44.8                                                                              41.0                                                                              43.7                                                                              40.3                                                                              37.0                                      Cure State  D   D   D   D   D   VD  VD                                        __________________________________________________________________________

The above data show that using 4 phr of reactive compound and a curetemperature of from 180°-185° C. that fully cured fibers possessingexcellent absorbent properties result. Because the absorbency propertiesusing 4 phr of reactive compound are not as good as the absorbencyachieved using 2 phr (see Table I), less than 4 phr cross-linking agentis preferred at a cure temperature of 180° C. and a cure time of about10 minutes. The data further show that if 4 phr of reactive compound isused, cure times of less than 10 minutes are required to achieve optimalabsorbency.

EXAMPLE 3

This example demonstrates the preparation of another syrup compositionof the invention (Syrup C) using substantially the procedure of Example1 but employing ISOBAM-18 rather than ISOBAM-10 copolymer. ISOBAM-18 hasa higher viscosity molecular weight of from 290,000 to 310,000.

Syrup C was observed to be non-cross-linked and found to be stable atroom temperature.

Fibers of 2-3 denier were spun from Syrup C by a dry spinning process.The effect of different cure temperatures and times on the absorbentproperties of three pairs (same cure times) of fiber samples is shown inTable III.

                                      TABLE III                                   __________________________________________________________________________    FIBER CURE CONDITIONS AND BRINE ABSORBENT PROPERTIES                          Fibers of Syrup                                                                           C   C    C   C   C   C                                            __________________________________________________________________________    Cure Temperature (°C.)                                                             174 178  174 178 174 178                                          Cure Time (Minutes)                                                                       4   4    6   6   8   8                                            Absorbency Test:                                                              Swell Index                                                                   Atm. Pressure (g/g)                                                                       74.7                                                                              118.8                                                                              126.9                                                                             122.5                                                                             118.5                                                                             96.0                                         0.5 psi (g/g)                                                                             44.2                                                                              68.7 80.2                                                                              71.8                                                                              71.8                                                                              63.7                                         Cure State  S   S/D  D   D   D   D                                            __________________________________________________________________________

The above data show the sensitivity of fiber absorbent properties tocure conditions. Although all of the six fiber samples were found topossess excellent absorbent properties, the data show that for Syrup C,the optimal conditions to be a cure time of about 6 minutes at a curetemperature of from 174°-178° C. The samples which were cured for only 4minutes were deemed to be slippery to the touch (S) and, hence,undercured.

EXAMPLE 4

Using the above-described procedures, three additional syrupcompositions (Syrups D, E, and F) were prepared using different reactivecompounds. Table IV sets forth the composition of Syrups D, E, and F andthe cure conditions and brine absorbent properties of the 2-3 denierfibers prepared from each syrup.

                  TABLE IV                                                        ______________________________________                                        SYRUP COMPOSITION,                                                            FIBER CURE CONDITIONS, AND BRINE ABSORBENT                                    PROPERTIES                                                                    Syrup Composition                                                                             D         E       F                                           ______________________________________                                        Copolymer:                                                                    Neutralized copolymer                                                                         100       100     --                                          of Example 1                                                                  Neutralized copolymer                                                                         --        --      100                                         of Example 3                                                                  Reactive Compound:                                                            Ethanolamine (phr)                                                                            3         2       --                                          DL-1-amino-2-   --        --      4                                           propanol (phr)                                                                Fiber Cure Conditions:                                                        Cure Temperature (°C.)                                                                 180       180     180                                         Cure Time (Minutes)                                                                           4         6       6                                           Fiber Absorbency Test:                                                        Swell Index                                                                   Atm. Pressure (g/g)                                                                           95.0      70.7    93.0                                        0.5 psi (g/g)   77.3      51.9    53.8                                        ______________________________________                                    

The above data show that excellent absorbency is achieved using variousreactive compounds which contain one amine and at least one hydroxylgroup.

It will be evident from the foregoing that various modifications can bemade to this invention. Such, however, are considered as being withinthe scope of the invention.

What is claimed is:
 1. A method for making absorbent fibers whichcomprises:(a) attenuating a partially neutralized, aqueous, uncuredpolymer composition prepared by reacting a strong base with a polymercontaining at least 25 mole percent recurring units of anα,β-unsaturated monomer having in its molecule one or two carboxylgroups or one or two other groups convertible to and converted tocarboxyl groups, the degree of neutralization of said partiallyneutralized polymer being within the range of from about 0.2 to about0.8 equivalent of total carboxyl groups or groups convertible to andconverted to groups of the α,β-unsaturated monomer, with from about 0 1to about 10 total parts by weight of at least one reactive compound per100 parts by weight of the partially neutralized polymer, the reactivecompound being a water soluble compound bearing one amine group and atleast one hydroxyl group, and (b) heating to cure and render themabsorbent by removing water and cross-linking through both ester andamide linkages.
 2. The method of claim 1 in which the composition isattenuated into fibers by a wet spinning process.
 3. The method of claim1 in which the composition is attenuated into fibers by a dry spinningprocess.
 4. The method of claim 1 in which the composition is attenuatedinto fibers by a flash spinning process.
 5. The method of claim 1 inwhich the fibers are cured and rendered absorbent by heating at atemperature within the range of from about 140° C. to about 210° C. 6.The method of claim 5 in which the fibers are cured and renderedabsorbent by heating at a temperature within the range of from about140° C. to about 210° C. for a period of from about 0.5 to about 20minutes.
 7. The method of claim 1 in which the heating step issufficient to produce a fiber capable of absorbing at least 60 times itsown weight of brine.
 8. The method of claim 1 in which the heating stepis sufficient to produce a fiber capable of absorbing at least 70 timesits own weight of brine.
 9. The method of claim 1 in which the heatingstep is sufficient to produce a fiber capable of absorbing at least 80times its own weight of brine.